Telephones are increasingly used for marketing due to cost versus success rate when compared with other advertising or sales media. Telemarketing has become a multi-billion dollar industry. As the use of telemarketing has increased, the intrusiveness and annoyance of such calls have begun to negatively impact the value of the underlying services. Consequently, many products and services are now available for screening these generally unwanted communications, and in 2003 DNC (Do-Not-Call) legislation was passed in the United States and has become one of the most popular government programs to date.
Call screening products and services have achieved some success but have been unable to meet subscriber expectations. One impact of DNC has been to reduce the volume of legal telemarketing calls, while actually increasing the volume of illegal and fraudulent calls from less ethical operators. With the introduction of internet telephony it is now possible for those operators to cost-effectively locate overseas where they can operate with impunity, and this is expected to happen.
Of course, telemarketers are frequently not the only type of unwanted calls. Even under DNC there are exempt calls that most people consider undesirable. As well, there are other categories of unwanted calls such as pranks, harassment, legal but undesired commercial contact, fraud, etc.
Screening solutions for unwanted electronic mail (e-mail) have become increasingly sophisticated and successful. Nevertheless, no long term solution has been shown to be effective because the originators of such e-mails aggressively search for and find new ways to get their messages through. In response, the e-mail screening solution providers also evolve their products to counter new tactics. However, the techniques required for screening unwanted real-time voice communications differ from those that work for e-mail. The reason is that less data is present in the initiation attempt of a real-time communications event than in an e-mail. An e-mail contains not only the addressing data that is comparable in some respects to real-time communications invitations, but also the entire content of the communication. Therefore screening of unwanted real-time communications can be significantly more challenging with respect to achieving a high level of reliability and accuracy. Further, the screening must be done in real-time so as not to delay or impair desirable communications. E-mail screening is not so constrained.